Exemplary embodiments relate to a method of writing for a nonvolatile memory device, and more particularly, to a method of writing using multiple band programs.
Generally, flash memory devices are nonvolatile semiconductor memory devices, which are electrically programmable and erasable. As demand for high speed, high density nonvolatile memory devices increases for mobile electronic devices requiring high density storage or coded memory, flash memory devices have become more popular.
Flash memory devices may be NAND type or NOR type. Generally, a memory cell array of NOR type flash memory has memory cells is connected to a bit line in parallel. On the other hand, a memory cell array of NAND type flash memory has memory cells connected to a bit line in series.
The program or read operation speeds of the NOR type flash memory are faster than those of NAND type flash memory due to the cell array structure, which makes the NOR type flash memory preferable when higher speed characteristics are needed. However, the NOR type flash memory is less integrated than the NAND type flash memory due to the cell array structure.
Multi-level flash memory devices are used to meet the need for higher density. A multi-level cell is able to store two or more bits, thus providing a solution to address limitations in flash memory devices. However, writing conditions are not sufficiently optimized to provide sufficient margins of threshold voltages of the memory cells in the multi-level flash memory devices.